SettlementWitness MCP

DefaultVerifier — SAR Verification Infrastructure

SAR (Settlement Attestation Receipt) is a verification protocol that produces cryptographically signed receipts proving whether an AI agent completed a task according to its specification.

DefaultVerifier is a live SAR verifier implementation with a public receipt registry, metrics API, and explorer.

If it matters—Verify it.

Architecture

Understand the SAR stack and verification model:

👉 SAR Architecture

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Example Response

{ "witness": "SettlementWitness", "witness_version": "v0", "task_id": "example", "verifier_endpoint": "https://defaultverifier.com/verify", "witness_timestamp": "2026-01-01T00:00:00Z", "receipt_id": "...", "receipt": { "profile": "settlement-witness-verified-v0.2", "task_id_hash": "sha256:...", "verdict": "PASS", "reason_code": "CONDITION_SATISFIED", "ts": "...", "verifier_kid": "...", "counterparty": "0xABC...", "receipt_id": "sha256:...", "sig": "base64url:..." },

"_ext": { "agent_id": "0x123:demo" } }

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Notes

• the receipt payload is issued under the settlement-witness-verified-v0.2 profile; verdicts are PASS, FAIL, or INDETERMINATE
• when counterparty is present, it is included in signature scope and in receipt_id derivation
• retired signer keys remain valid for verifying receipts they historically signed; verifier_kid in a receipt is historical evidence and is never rewritten
• current signer lifecycle (which kid is active vs. retired) is published at https://defaultverifier.com/.well-known/sar-keys.json — treat that endpoint, not this README, as the source of truth for which key is currently active
• this behavior is implemented and publicly verifiable via the live receipt and key endpoints

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SAR Compatibility: This implementation follows SAR verification semantics, with an extended signed payload when counterparty is present.

Demo

Run a full end-to-end verification in ~2 minutes: DEMO.md

Quick Start

1. Create a receipt

curl -X POST https://defaultverifier.com/settlement-witness
-H 'content-type: application/json'
-d '{ "task_id":"quickstart-001", "spec":{"checks":[{"kind":"field_equals","inputs":{"output_path":"$.result"},"expected":"hello"}]}, "output":{"result":"hello"}, "counterparty":"0x1234567890abcdef1234567890abcdef12345678" }'

2. Fetch the receipt

curl https://defaultverifier.com/settlement-witness/receipt/<receipt_id>

Note: use the receipt_id from the returned receipt

3. Verify locally (Node)

cd examples/node-verify node verify.js receipt.json jwks.json

Examples

Node.js verification example: examples/node-verify/

Python verification example: examples/verify_receipt_python.py

Usage: python3 examples/verify_receipt_python.py <receipt_id>

API Endpoints

Create Receipt

POST /settlement-witness

Submits a task verification request and returns a signed SAR receipt.

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Retrieve Receipt

GET /settlement-witness/receipt/{receipt_id}

Note: Use the receipt_id from the returned receipt (sha256:...) for retrieval.

Returns a previously issued receipt.

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Wallet Receipt Explorer

GET /settlement-witness/receipts?wallet={address}

Returns recent receipts associated with a wallet address.

The public explorer is available at:

https://defaultverifier.com/explorer

This interface allows browsing recent receipts and wallet-indexed delivery history.

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Public Verification Keys

https://defaultverifier.com/.well-known/jwks.json

Alternative (SAR protocol reference): https://defaultverifier.com/.well-known/sar-keys.json

Used to verify Ed25519 signatures for receipts.

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Key Registry

https://defaultverifier.com/.well-known/sar-keys.json

Registry of verifier public keys referenced by verifier_kid.